Study On Hot Tearing Susceptibility Of Mg-Zn-Cu-Y Alloys

Lightweight,versatility and environmental protection have become a significant trend in the development of the new era.Magnesium alloys have gradually been used in various fields due to their advantages such as low specific gravity,high specific strength and specific rigidity,good electromagnetic wave shielding,and easy recycling rate.However,the magnesium alloy has a wide solidification interval,and the structure of its castings is becoming more and more complicated.Therefore,to expand the scope of application of magnesium alloys in actual production,studying the thermal cracking mechanism of magnesium alloys and reducing their thermal cracking susceptibility has become the primary task to be solved.Based on the Clyne-Davies theoretical model,this paper predicts the hot tearing susceptibility of Mg-Zn-Cu-Y alloys.The effects of changes in the Y content of the Mg-6Zn-1Cu-xY-0.6Zr?x=0,1,2,3,6wt.%?Alloy on the hot tearing susceptibility of the alloy and Mg-4.5Zn-xCu-6Y were studied-0.6Zr?x=0,1,2,3wt.%?The effect of Cu content change on the alloys hot tearing susceptibility.Mainly studied after adding different contents of Y and Cu elements,the microstructure of the alloy,the characteristics of the solidification path,the temperature change of the dendrite coherence point and the influence of the Mg-Zn-Cu-Y alloy hot tearing susceptibility.In this paper,the dual thermocouple test method is used to collect the characteristic parameters of Mg-Zn-Cu-Y alloys with different contents of Y and Cu added during the solidification process;the"T"type hot cracking mold test system is used to add Mg with different contents of elements-The solidification shrinkage stress of Mg-Zn-Cu-Y series alloy is collected with the change temperature of solidification temperature,which is used to study the specific time node of hot cracks generated during the solidification process of magnesium alloy and analyze the occurrence and expansion mechanism of hot cracks;X-ray diffraction?XRD?and Scanning Electron Microscope?SEM?respectivelyforMg-6Zn-1Cu-xY-0.6Zr?x=0,1,2,3,6wt.%?Alloyand Mg-4.5Zn-x Cu-6Y-0.6Zr?X=0,1,2,3wt.%?The microstructure of the alloy and the micromorphology of the fracture area were observed.The effects of the type and number of second phases precipitated at the grain boundaries of Mg-Zn-Cu-Y alloys,the change in grain size,the solidification path of the alloy,and the temperature of dendrite coherency temperature on the susceptibility of the alloy to hot cracking were studied.The results show that with the addition of Y element,the dendrite coherency temperature decreases significantly,from 619°C without Y element to about 600°C.The lower dendrite interference temperature is usually due to the shorter dendrite arms resulting in a shorter dendrite overlap time.The fine grains of the alloy are more conducive to the shrinkage between dendrites.Then through the measurement of the grain size,as the Y content increased from 0 wt%To 6.0 wt%,The average grain size of the alloy decreased from 79.5?m to 40.3?m.Moreover,through microscopic observation of the cracks,we can find that with the continuous increase of Y content,the content of the liquid phase that can be freely packed at the late stage of alloy solidification also increases significantly.Through EDS analysis,it is found that a large amount of residual liquid content Y element,which can also prove that the addition of Y element can effectively reduce the hot tearing susceptibility of the alloy.For the Mg-4.5Zn-xCu-6Y-0.6Zr?x=0,1,2,3wt.%?alloy,the increase in the content of Cu element changes the type and precipitation amount of the second phase.The LPSO phase can reinforce the grain boundary but the packing ability is insufficient.With the addition of Cu,the LPSO phase disappears,and the W phase?Mg₃Zn₃Y₂?and Mg₃?ZnCu?₃Y₂ phase with strong packing ability appear.There is also a quasi-crystalline phase I?Mg₃YZn₆?co-lattice with the?-Mg matrix.The alloy not only has good shrinkage ability but also has good intergranular strength.The hot tearing susceptibility of the alloy is greatly reduced.